totm nov 2023 SpaceX Discussion Thread

[tater]

At least this only sets things back a few weeks. We watched it (the nose) appear from nothing.

[DDE]

33 minutes ago, NSEP said:

Uh oh.

Hello darkness, my old friend...

 

[tater]

 

 

 

[Ultimate Steve]

RIP Starhopper fairing.

 

[Terwin]

Just now, Ultimate Steve said:

RIP Starhopper fairing.

 

You forget, steel is easy to hammer back out, it would only be useless if it were damaged(or potentially damaged) carbon fiber.

One of the advantages of steel is the ease of working with it.  Make a mistake and the worst you need to deal with is a bit of hammering and careful welding.

[Spaceception]

Well, I guess that "unforeseen" issue happened

[cubinator]

That's too bad it fell over, but I'm glad it's far from irreparable.

[StrandedonEarth]

Dented and hammered out equals extra work hardening, leftover wrinkles add stiffness at the potential expense of aerodynamics. Time to call the local bodyshop 

[tater]

3 hours ago, Terwin said:

You forget, steel is easy to hammer back out, it would only be useless if it were damaged(or potentially damaged) carbon fiber. 

One of the advantages of steel is the ease of working with it.  Make a mistake and the worst you need to deal with is a bit of hammering and careful welding.

Yeah, that's not gonna hammer out, easier to build a new fairing I think.

EDIT--Added a pic:

 

 

Edited January 23, 2019 by tater

[DDE]

18 minutes ago, tater said:

Yeah, that's not gonna hammer out, easier to build a new fairing I think.

Tell that to the Proton. The new parts need hammering out to fit; there reportedly was a big scandal when the issue was rectified and the two guys who’d been fixing that exact issue in every flight article for thirty years were laid off.

[tater]

 

[sh1pman]

Oh, I can see the headlines of “news pieces” on big media sites tomorrow. “Musk’s tinfoil starship blown over by winds!”, etc.

[sevenperforce]

The one silver lining is that the accident prompted Elon to identify the top piece as a fairing, specifically. This strongly implies that even the cylindrical portion of the "upper" piece will be empty; until now, it was uncertain whether tankage might protrude upward.

This, along with some higher-quality drone footage, means we can now do a little more evaluation.

This shot shows the placement of what appears to be the central bulkhead separating LOX from CH₄. 

Possible tracing of bulkhead outline:

We already know that the upper bulkhead has been sitting outside, waiting to be added, which means it will be added on top of the triangular leg support beams:

The beams will be therefore be immersed in the liquid methane.

A possible cutaway:

Anyone with more time than me want to run the numbers and see what kind of propellant volume we're potentially looking at?

The placement of the upper and lower bulkhead is a guesstimate; the placement of the central bulkhead is placed by visual/pixel count on the most recent image. Remember that liquid oxygen is 2.4x more dense than liquid methane and the Raptor will use 3.8x as much LOX by mass.

[Racescort666]

48 minutes ago, sevenperforce said:

Anyone with more time than me want to run the numbers and see what kind of propellant volume we're potentially looking at?

Gotchu fam:

• Upper Tank (fuel right?): 778 m^3
• Lower Tank (oxidizer): 261 m^3

I may have screwed this up but I used my tried and true scaling the picture in powerpoint technique.

[sevenperforce]

2 hours ago, Racescort666 said:

Gotchu fam:

• Upper Tank (fuel right?): 778 m^3
• Lower Tank (oxidizer): 261 m^3

I may have screwed this up but I used my tried and true scaling the picture in powerpoint technique.

For some reason I was thinking that the upper tank would be methane and the lower tank would be LOX (I guess I was thinking in terms of tailfirst stability on landing) but that's completely wrong. Upper tank (which will bathe those triangular members) is LOX, as with Falcon 9 S1 and S2; lower tank is methane.

If mixture ratio is 3.8:1 and LOX is 2.4x as dense as liquid methane, then the volumetric ratio should be 1.58:1, which makes sense.

That being said, the values above give a volumetric ratio of almost 3:1, which is twice what it should be.

When I just measured and calculated, I got 264 cubic meters for the lower tank and only 441 cubic meters for the upper tank (9.76 in the lower tube + 43.85 for each 9x2 spherical cap + 343.5 for the central cylinder) which comes to a volumetric ratio of 1.67:1 which is within 6% of where it should be, which is pretty bloody close for a pixel-count from a blurry drone shot. Upper tank will hold slightly less propellant because it has those triangular supports in it, which brings it even closer to perfect.

This would translate to an upper-bound fuel mass of 111 tonnes and an oxidizer mass (sticking with the 3.8:1 mixture ratio) of 421 tonnes for a total propellant mass of 531 tonnes. If we guess the hopper at around 75 tonnes dry, that gives us a GLOW of 606 tonnes. Three Raptors produce 611 tonnes of thrust.

At a SL Raptor isp of 330 s, that's 6.76 km/s of dV.

[CatastrophicFailure]

Nice close up here. Apparently the tower’s been painted black *cue sitar.*

[RedKraken]

If your oxidiser tank is 261 m^3,  your CH4 only needs to be ((261/0.54) - 261) = 222 m^3 to get 3.6 O/F ratio.

Sev is using 3.8, not really a big difference in this case.

(Volume ratio for 3.6 is roughly 54% lox, 46% CH4.)

483 m^3 total 

bulk methalox subcooled is ~ 900kg per m^3

so 483 * 0.9 = 435t

 

On the other hand,

if the methane tank is 261 m^3, your oxidiser should be (261/0.46 - 261) = 306 m^3

567 m^3 total

so 567 * 0.9 = 510t

 

I'm going to use a much lighter hopper mass (given the fairing blew over, doh) than sev.

Based on 3.5mm average thickness SS, rather than the 5mm i was using before. Fairing will be much less thick. Base will be much more.

I read somewhere NSF? in the last day that tank pres (3atm?) will require about 3.5mm for the starship tanks. Hopper could get away with less.

I'm starting to think it will be around 40t.

510 t prop, 40t dry , 330s is about 8500 m/s deltaV.

Thats a lot of dv.....flying low will average slightly above 330s isp too.

Edited January 23, 2019 by RedKraken

[MaverickSawyer]

So.... It has enough dV to do some pretty spectacular suborbital hops, doesn't it?

[cubinator]

24 minutes ago, MaverickSawyer said:

So.... It has enough dV to do some pretty spectacular suborbital hops, doesn't it?

Put some seats on it and take me to Brazil, that's almost orbital.

[DDE]

5 hours ago, sh1pman said:

Oh, I can see the headlines of “news pieces” on big media sites tomorrow. 

Just go take a look at the Trotskyist hellhole that is by now r/EnoughMuskSpam.

[sevenperforce]

This one will not go suborbital -- unlikely to break 5 km. No need to go suborbital because they don't have the systems to test entry and descent anyway.

But yeah, it potentially has a LOT of dV.

57 minutes ago, RedKraken said:

On the other hand,

if the methane tank is 261 m^3, your oxidiser should be (261/0.46 - 261) = 306 m^3

567 m^3 total

so 567 * 0.9 = 510t

My upper tank size was an upper bound, but if we assume that the upper bulkhead is mounted flush with those triangular supports rather than at the top of the base, that shaves off 72 cubic meters of volume. Let's round it up to 80 to account for volume displaced by the supports themselves. That puts a lower bound on upper-tank size at 361 cubic meters or 412 tonnes. At 3:8 (less generous from this perspective than @RedKraken) you get total prop mass of 520. With my dry mass that gives 7.1 km/s dV; with @RedKraken's it's 8.5 km/s.

[tater]

 

[Ultimate Steve]

Can it even be called a cone any more?

[RedKraken]

I feel a bit flat.....like the hopper fairing.

https://twitter.com/RogerLewisHolt/status/1088211714863218688

Edited January 23, 2019 by RedKraken

[DAL59]

I just just checked in on starship news after several days, how did a mere 50 mph wind blow it over?  Isn't this supposed to withstand max-q?